A scar forms in response to cutaneous injury as part of the natural wound healing process. It is a lengthy and continuous process, although it is typically recognized as occurring in stages. The wound healing process begins immediately after injury, with an inflammatory stage. During this stage, which typically lasts from two days to one week (depending on the wound), damaged tissues and foreign matter are removed from the wound. The proliferative stage occurs at a time after the inflammatory stage and is characterized by fibroblast proliferation and collagen and proteoglycan production. It is during the proliferative stage that the extracellular matrix is synthesized in order to provide structural integrity to the wound. The proliferative stage usually lasts about four days to several weeks, depending on the nature of the wound, and it is during this stage when hypertrophic scars usually form. The last stage is called the remodeling stage. During the remodeling stage the previously constructed and randomly organized matrix is remodeled into an organized structure that is highly cross-linked and aligned to increase mechanical strength.
The changing patterns of the connective tissue matrix during repair following injury require a delicate balance between synthesis and degradation of collagen and proteoglycans. Under normal circumstances this balance is maintained, while in many diseased states, it is altered, leading to an excessive deposition of collagen, to a loss of functional tissue, or to disfigurement. With hypertrophic scars and keloids, the biosynthetic phase continues longer than necessary to repair the wound. In order to maintain nutrient supply, vascular in-growth occurs, resulting in large, highly vascularized scars which are unsightly and can be disabling. Keloids and hypertrophic scars result in functional and cosmetic deformity. They are a common clinical problem.
While the histological features characterizing hypertrophic scars have been well documented, the underlying pathophysiology is not well known. Hypertrophic scars are a side effect of excessive wound healing, and generally result in the overproduction of cells, collagen, and proteoglycans. Hypertrophic scars are thick and take the form of a raised scar on the skin as a result of overproduction of cells, collagen, and proteoglycans.
A keloid is a raised scar that exceeds the boundaries of the initial injury (unlike hypertrophic scars which typically stay within the wound boundaries), and is rarely corrected by surgical intervention. Keloids are typically characterized as tumors consisting of highly hyperplastic masses that occur in the dermis and adjacent subcutaneous tissue in susceptible individuals, most commonly following trauma. Keloids may grow into a firm lump that is many times larger than the original scar and are typically fibrotic growths that contain a collection of atypical fibroblasts and an increased abundance of extracellular matrix components, especially collagen.
Keloids are often more severe than hypertrophic scars, since they tend to invade normal adjacent tissue, while hypertrophic scars tend to remain confined within the original scar border.
Although commonly benign, hypertrophic scars and keloids often cause discomfort, pain, pruritus, physical disfigurement and impaired quality of life.
Most of the scar reduction products contain silicone in a sheet or gel format, and onion extracts (Mederma Skin Care products). It usually takes over 3 months to see some effect, because these products do not contain effective active ingredient such as any form of collagenase which targets the cause of scar formation. See www.mederma.com/learning/caring_for_scars.
Other attempts to treat hypertrophic scars and keloids include surgery, mechanical pressure, steroids, x-ray irradiation and cryotherapy. There are many disadvantages associated with each of these methods. Surgical removal of the scar tissues is often incomplete and can result in further development of hypertrophic scars and keloids at the incision and suture points. Steroid treatments are unpredictable and often result in depigmentation of the skin. X-ray therapy is the only predictable effective treatment to date; however, because of its potential for causing cancer, it is not generally recommended or accepted. The most common approach to controlling scar, and in particular excessive scar formation, is to apply pressure, which appears to be somewhat effective in many instances. This treatment has limited application, generally based on the size and location of the scar tissue on the body. Other commonly used treatments are application of Vitamin E and corticosteroids.